Impact switch



April 19, 1960 B. MCCOLLUM IMPACT SWITCH Filed March 18. 1957 TIME 5a/fon MC C0 //um INVENTOR.

l mu u United StatesPatent O ice Mzasoo Y MACT SWITCH y i Burton McCollum, Houston,v Tex. Application March 18, 1957, Serial No. 646,838

` 1 claim. (c1. :s4-1) My present invention is aswitch designed to respond or changerposition at the exact moment of maximum acceleration, either positive or negative, `of a moving bodyv to Whichmit is att-ached. It is `suitable for use in all installations inwhich an accurate'deter-mination of such an event is desired. t

My switch is particularly useful in the art of exploring subsurfaceA geology by means ofl :the seismograph `and resultsin-the attainment ofmore accurate timing ofthe seismic impulses than `has beenaccomplished heretofore; It is specifically adapted to the method of generation of seismic waves by the dropping of aweight as set out in my copending applications Serial No, 413,297, Vfiled March 1 1954 now Patent No. 2,851,121, andSerial No. 423,347, tiled April 15, 1954 now- Patent No. 2,851,122. In those applications there is described a procedure for generating seismic waves by dropping a largepweight from4 a height of a few feet. Since the major part of the seismic impulse is generated at the time the pressure of the Weight against the ground is greatest; it 4is impoitant that any timing device used to indicatethetimeof this impact `be responsiveto'the maximum pressure. In the method of timing the seismic waves outlined in the above applications, there is described an electricalftiming device comprising a body which is affixed to the falling weight. Within this body -is a contactterminal whichis movable relative thereto. *The terminal is heldin a normally closed position by a spring until such time as thedeceleration, Vi.e.,` negativefacceleration, of the weight reaches such magnitude that the movable tenninalpvercomes the spring' force and yrnoves'away from its contact point,`

thereby breaking the circuit. In other words, thev device is designed in such a manner that the contact willV open atl some predetermined value of negative acceler- This device works well under many conditions, but experience shows that in certain casesl it does not give a suicently accurate indication ofthe time of generation in Figs. 1 and 2 of the drawing, wherein:

v Fig. 1 is a diagram showing how the negative acceleration of a mass varies as a function of time when it strikes ground having a hard surface;

t of the seismic energy. The reason for this is illustrated deceleration point.

2,933,300 Patented Apr. 19, 1960 Y, 2 plowed eld, a very diierent situation exists, as illustrated in Fig. 2.v The moment the weight/touches the surface Vthere is a certain amount of pressure, and a corresponding amount of deceleration, as at 4, which is usually too small to cause the Vabove described switch to open. As

v the ground surface is compressed, it develops increasing resistance, causing the deceleration to increase progressively as shown by the parts of the curve 5 and 6 until `4, 5 or` 6, depending on lthe values of negative accelera-` tionV attained at those points. If the spring is` adjusted for an operating curve such Fig. 1, it may fail to openwhen the weight is dropped on a soft and yielding surface because of the relatively low value of the peak Even when the switch functions the error in the time of opening of the contact due to the above cause may bel aspmuch as 5 to 10 milliseconds, a very objectionable uncertainty. Y l y Therefore, it is an object of my invention to provide Y a switch which will function to determine the maximum acceleration, either positiveor negative, of a moving body, independently of .the magnitude of such acceleration.

More specifically, it is an object of my invention to provide a switch which will respond to the maximum impact of a falling weight, regardless of the surface conditions of the resisting medium.

It is also an'object of my invention to provide a switch of-thedescribed ltype which is simple in operation, rugged, and economical. y

My present invention is basedl on the presumption, well borne out -by experience, that the moment of effective generation of a seismic wave by a falling body coincides with the time of the peak of deceleration of the body, that is,at the point 2 in Fig. 1 or the point 7 in Fig. 2,

and my switch is designed to signalv an event that alwaysVV will beassociated closely `with this peak of deceleration. t l prefer to ,employ a sensing device which generates a current in an electricalfcircuit vwhichgiis connected to the solenoid of a normally closed polarized relay. The direction of the current in 'the solenoid is reversed as vthe accelerating force acting on the sensing device passes its peak, and the relay is -thereby opened.

The -basic elements of my switch areshown in Fig. 3 in a diagrammatic View. For the'purpose of illustrating one of its applications, .the sensing device l0, similar to --an ordinary telephone receiver, is xed to aibody 11 mov,-

ing in the direction shown by arrow 12. vIn the sensing device, a soft iron diaphragm 13 serves the double purpose of armature and vinertia weight in the magnetic circuit established by permanent magnet 14 and its two associated pole pieces 15 and 16. The pole pieces are of a soft magnetic material such as soft iron. In the arrangement shown, any deceleration of the moving body 11 causes the diaphragm 13 to move downward away from the pole pieces 1S and 16, thereby reducing the the point 1 to a maximum at 2 and then falls off rapidly to a relatively low value in the `interval between 2 and 3. lf the surface conditions are nearly ideal, i.e., very hard and compact, the peak of the curve will occur in no more than one or two milliseconds, Vand the switch will open during this brief period and give a satisfactory indication of the 'time'. of generation of the seismic wave. However, if the surface Yon which the weight falls is soft and yielding, asin the Acase of a thick bed of soft sand Lor a magnetic iiux linking with the surrounding interconnected coils 17 and 13 and inducing a voltage therein. It will readily be seen that as long as the deceleration is increasing, therewvill be a current moving in a certain direction in the coils 17 and 18 because the diaphragm 13 is receding farther and farther away from the pole pieces. While the lbody 1'1 is at rest or while its deceleration remains constant, no voltage or current will be ind-uced. However, if the deceleration starts to diminish,

Y awww 2.and'7 of VFigs...A 1 and` 2-respectively, the direction of the induced current will-be reversed by movement of the diaphragm toward the pole piecesl If now we bring the leads 19 out, preferably through an amplifier 20, to Y which the negative accele'raion increases, the contact .Z3 jwill remain closed. However, after the deceleration passes a maximum, a reversecurrent is sent through the solenoid 21 of the relay 22 whichopens thcscontact 23, thereby signalling the instant that-most precisely coincides the Ytime of `generation of the seismic wave.

In order for thefarrangement above `outlined to tfunction `etiiciently, :the-natural lfrequency of4 the Vdiaphragm 13 should be very high, preferably :several thousand 'cycles per second or higher.v I prefer also to insert in the'circuit between ,the sensing element `and the amplifier alow pass filter exemplified 4by the condenser and the inductor A25. This will virtually eliminate the undamped vibrations ofvthediaphragm 13 and permit only a current characteristic ofthe decelerationrate to flow. Alternatively, a suitable vdamping iiuid can be placed inside the sensingtdevice to give critical damping tothe diaphragm 13.

I have chosen to illustrate but a single application of my switch, and it is apparent that the .structure described will mark lthe moment of maximum positive or negative acceleration of Vany body to which it is aixed, the positive peak being evidenced by ,a closing of the relay. Further, by reversing the connection of the leads to the solenoid of the polarized relay, the device can be made to indicate maximum negative Aacceleration `.by a closing of the relay and maximum positive acceleration by an opening of the-relay. A substitution of a normally open relay for the normally closed relay also will result in a workable device, this innovation also being .embraced within the present invention. Y

I prefer to usea polarized relay to mark the exact moment of the-reversal of current. However, vthe movement of the sensing device inertia weight could be used to modulate the currentir an electrical circuit as by electrostatic or electromagnetic induction, the making or breaking Aof van velectrical contact as described above being a special case of 'such modulation.

Obviously, any vtype'of accelerometer, whether employing varying resistance, piezoelectric properties,` or mag'- netostriction, can be adapted to accomplish the purpose herein set out if it produces a current which reverses in direction as the acceleration of the body to which it is attached passes its peak. The essence of my invention rests vbroadly in the use of any similar principle whereby the direction of the induced current is detected by electrical current responsive means to indicate the instant of maximum acceleration, either positive or negative, of the body to which the accelerometer is attached. Accordingly, it is desired to protect by Letters Patent all forms of .the invention falling within the `scope of the following claim.

I claim:

In seismic e.\:ploration, apparatus for indicating the instant of maximum negative acceleration of a vertically decelerating body comprising a current generating element attached Atosaid body, said current" generatingelement comprising :a permanent magnet, polepieces associatedtherewith, an inertia elementadiacent said pole pieces and adapted for vvertical movement in opposite directions Vrelative thereto in response to increasing and decreasing negative acceleration, and a coil within the magnetic iiel'd of said permanent magnet; and a-polarized relay electrically connected to the said coil so as to change position` at the instant of reversal of direction of thec'urrent produced Yby said current generating element.

References Cited in the le of this patent UNITED STATES PATENTS y1,948,104 Paesane r. Feb. 20,.-1934 2,574,600 4stores Nov; 13, -195.1 2,643,869 Clarkv 1111123111953 l y, FOREIGN PATENTS 847,119 Germany Aug. 21, 11952 OTHER REFERENCES A new` electro-magnetic seismograph (Beniol),from Fifth 'PaciIicScience Conference, 1935 (pages 2443- 2450).

Gough: A YNew 'Instrument for Seismic Exploration at Very Short Ranges, Geophysics Magazine,-vol. 17, April '1952, pages'31'1-'32L 330433. l

A Newl Approach to Seismic Exploration (Palmer), -from World0il,' volume 138, No. 7,v June 1954 (pagesy 1,40 and 142). 

